When you have undigested meat proteins in your colon, they will basically do what they do when thery are outside the colon: they rot. The rotting, or decay, is characterized by a release of foul-smelling chemicals.
One such chemical is cadaverine--the same that gave "cadavers" their name because of the smell they emit--which is the result of protein hydrolysis or the decarboxylation product of lysine. It's similar in structure to putrescine, putrescine itself produced from rotting activity.
Rotting flesh in the colon gives off a horrible odor and the smelly chemicals can become apparent in a person's breath, feces or urine. The person may suffer from the foul odors for a good while as the long process digestion or elimination of the meat continues.
To help speed things along, it's important to maintain a diet high in dietary fiber, specifically insoluble fiber, which helps increase rate of transit in the colon. Insoluble fiber comes from the "woody" parts of plants such as wheat bran and vegetable skins.
No one should have to put up with "the smell of death" after a meal. To avoid offensive gas and bad breath, just eat smaller portions of meat and be sure to also include some salad and extra vegetables.
Lecture notes by Albert Grazia, M.S.